Homogenization is the breaking down and mixing of the components of an emulsion or dispersion. A major use of homogenizers is to break down and disperse milk fat into the bulk of skim milk. This delays creaming of milk fat globules. Homogenizers are also used to process other emulsions such as silicone oil and to process dispersions such as pigments, antacids, and various paper coatings.
In the most widely used type of homogenizer, the emulsion is introduced at high pressure of from 500 psi to 10,000 psi to a central bore within an annular valve seat. The emulsion is forced out through a narrow gap between the valve seat and a valve plate. Through the gap, the emulsion undergoes extremely rapid acceleration as well as an extreme drop in pressure. This violent action through the valve breaks down globules within the emulsion to produce the homogenized product.
The degree of homogenization is a function of the difference between the pressure of the emulsion at the inlet to the valve and the pressure at the outlet. Past systems for homogenizing milk have, for example, used an inlet pressure in the order of 2,000 psi. Recently, in an effort to conserve the amount of energy required to homogenize milk and other products to a predetermined degree, attempts have been made to reduce that required homogenizing pressure. Such attempts have not resulted in the same degree of homogenization possible with higher pressures. An object of the present invention is to provide a method and apparatus for homogenizing to a desired degree but at lower pressures than has heretofore been possible. By homogenizing at lower pressures, less energy input is required at the liquid pump.
The exact mechanism by which homogenization occurs is not absolutely known; however, current theories and experimental evidence indicate that cavitation and turbulence are the primary forces responsible for the homogenization phenomenon. Based on those theories, Hans-Albert Kurzhals has concluded that a knife edge valve seat provides optimal valve geometry. Kurzhals used a knife edge valve in which the travel distance through which the fluid accelerated was about 0.004 inches. His experimental work was limited to the low flow rates of a laboratory environment, however.
Also relying on the cavitation theory, Ching C. Loo had previously designed a homogenizing valve having an annular knife edge valve seat spaced 0.001 inch from an opposing valve surface. In his U.S. Pat. No. 2,882,025, Loo suggested a stacked configuraion of valve members. Despite his ability to obtain homogenization at low pressures, the Loo homogenizer has not gained wide acceptance.
A further object of this invention is to provide a commercially acceptable homogenizing method and apparatus for homogenizing emulsions and dispersions at flow rates of up to the order of 14,000 gallons per hour at a substantially reduced homogenizing pressure than is conventionally used.